On a magnetic-recording disk which is used in a disk drive, servo patterns are formed at given circumferential locations. These servo patterns represent data for indicating the approach of a track and data for indicating the deviation of a magnetic-recording head relative to a track where the servo pattern was formed. One method for forming these servo patterns, known by the term of art “self-servo writing,” forms servo patterns on a magnetic-recording disk, utilizing a positioning mechanism of a magnetic-recording head provided by the disk drive, itself.
The self-servo writing method takes advantage of the fact that a write element and a read element in the magnetic-recording head are disposed, such that each is separated from the other along a radial direction of the magnetic-recording disk. The self-servo writing method sequentially forms servo patterns at given circumferential locations on the magnetic-recording disk by repeating a process that includes reading data from a previously formed servo pattern read by the read element of the magnetic-recording head to position the magnetic-recording head for forming a new servo pattern with the write element of the magnetic-recording head.
However, under circumstances such that there is a faulty servo pattern from which data cannot be read, for example, because the servo pattern was formed on a defect of the magnetic-recording disk, positioning of the magnetic-recording head would fail so that forming servo patterns at given circumferential locations on the magnetic-recording disk is hindered.